An edge-emitting semiconductor laser (diode-laser) is formed by defining an emitting region in a separate-confinement heterostructure epitaxially grown on a single-crystal substrate. The emitting region is commonly referred to as a “stripe” by practitioners of the art. The strip typically has a length between about 1.0 and 1.5 millimeters (mm), and emits radiation from an emitting “aperture” having a height of about 1.0 micrometer (μm) and a width between about 4 μm and 200 μm. The aperture width is usually referred to in the art as the emitter-width or stripe-width. A diode-laser having an emitter-width greater than about 30 μm is often referred to as a wide-emitter or wide-stripe diode-laser.
Generally, for a given length of a diode-laser, the greater the stripe (emitter) width, the greater will be the potential output power of the diode-laser. However, the greater the stripe width, the greater is the number of transverse modes at which the laser delivers output radiation. The greater the number of transverse modes, the poorer is the quality of the output beam of the diode-laser. While a multiple transverse mode output beam is acceptable for diode-laser applications such a heating and surface treatment, it is often not suitable for applications in which the output beam must be focused into a small spot, for example in end-pumping a fiber laser. There is a need for a separate confinement heterostructure that provides for improved beam-quality in a wide-stripe diode-laser.